At present, general plant transformation is carried out via direct introduction of a foreign gene into a callus or a piece of tissue in an in vitro culture system via Agrobacterium tumefaciens or by particle bombardment. However, such techniques are insufficient in terms of transformation efficiency, and thus requires marker selection through the introduction of a selectable marker gene. In contrast, expression of a selectable marker gene may influence the phenotype of a resulting transformed plant, and it is preferable from the viewpoint of safety that a transformed plant does not comprise a selectable marker gene. Accordingly, development of transformed plants without the introduction of selectable marker genes is desired.
A floral-dip method by which plant transformation is carried out without the use of a callus or a piece of tissue in an in vitro culture system has been known as a technique for transformation of Arabidopsis thaliana. Because of low transformation efficiency, however, there have been substantially no reports of application of such technique to other plant species. Patent Document 1 and Non-Patent Document 1 disclose versatile methods of in planta transformation that enable transformation via the in planta method without in vitro culture of plant cells. However, such techniques remain problematic in terms of transformation efficiency.